Note: Helix or no helix of β-peptides containing β 3hAla(αF) residues?

摘要

A remote ~4J(F,H) coupling (F-C(α)-C(O)-N-H) of up to 4.2 Hz in a-fluoro amides with antiperiplanar arrangement of the C-Fand the C=O bonds (dihedral angle F-C-C=O ca. 180°) confirms that previous NMR determinations, using the XPLOR-NIH procedure, of the secondary structures of β-peptides containing β~3hAla(αF) and β~3hAla(αF_2) residues were correct. In contrast, molecular-dynamics (MD) simulations, using theGROMOS program with the 45A3 force field, led to an incorrect conclusion about the relative stability of secondary structures of these b-peptides. The problems encountered in NMR analyses and computations of the structures of backbone-F-substituted peptides are briefly discussed.